Frailty in asthma-COPD overlap: a cross-sectional study of association and risk factors in the NHANES database

Background Asthma-chronic obstructive pulmonary disease (COPD) overlap (ACO) is a condition characterised by the simultaneous presence of features of both asthma and COPD. The study aims to investigate the association between ACO and frailty among middle-aged and elderly populations, and identify the risk factors for frailty in individuals with ACO. Methods We conducted a cross-sectional study with 34 403 eligible participants (aged ≥40 years) from the National Health and Nutrition Examination Survey 1999–2018 cycles. Participants were stratified into four groups: ACO, asthma, COPD and non-asthma/COPD. Frailty assessment was based on frailty index, generating frail and non-frail group. Univariate and multivariate survey-weighted logistic regression analysis were used to determine the association between ACO and frailty, and to identify the risk factors for frailty in ACO. Results The frailty prevalence in participants with ACO was 60.2%, significantly higher than that in those with asthma (32.3%) and COPD (40.6%). In the unadjusted model, participants with ACO exhibited six-fold higher odds of frailty (OR 6.30, 95% CI 5.29 to 7.49), which was significantly greater than those with COPD (OR 2.84, 95% CI 2.46 to 3.28) and asthma (OR 1.99, 95% CI 1.80 to 2.18), using the non-asthma/COPD group as a reference. After adjusting for all confounders, participants with ACO had over four times higher odds of frailty (OR 4.48, 95% CI 3.53 to 5.71), still higher than those with asthma and COPD. The findings remained robust in sensitivity and subgroup analyses. Furthermore, hypertension, cancer, cardiovascular disease, chronic kidney disease and cognitive disorders were identified as risk factors for frailty among ACO participants, while higher income and education levels were protective factors. Conclusion Patients (aged ≥40 years) with ACO were at a higher risk of frailty, regardless of age or sex, compared with those with asthma or COPD alone. Greater attention should be paid to patients with ACO, regardless of their age.